As a method for sensing an object or obstacle at a short distance, sensors are widely used in industry. A sensor irradiates infrared (IR) light into a sensing area and measures reflected light so as to sense an object or obstacle in the sensing area.
Recently, there has been developed a technique for measuring the position of an object by obtaining an IR image using an image pickup device. In a method of sensing an object at a short distance through the technique, a certain amount of light is first irradiated into a sensing area through photometric illumination, and the light reflected and returned from an object or obstacle that exists in the sensing area is then filtered through an IR filter, so that an IR image is obtained through an image pickup device. Subsequently, the obtained IR image is analyzed, thereby detecting the position of the object or obstacle that exists in the sensing area.
However, in the related art, in a case where another luminous object exists in the exterior of the sensing area in addition to the photometric illumination, the light irradiated from the photometric illumination is mixed with light generated from the external luminous object. The mixed light is reflected from the object, and the mixed reflected light can be picked up by the image pickup device. Therefore, an IR image by the external object may be recognized as the object that exists in the sensing area, and accordingly, an IR sensor may be erroneously operated.
As an example, when the IR sensor is used outdoor, it is difficult to distinguish an IR image by sunlight from an IR image by photometric illumination. Furthermore, since the sunlight is a strong IR light source, the IR sensor may erroneously recognize the IR image reflected from a long-distance object by the sunlight as the object that exists in the sensing area.
As another example, when the IR sensor is used indoor, it is also difficult to distinguish an IR image by the photometric illumination from an IR image generated by lighting illumination transmitted to window or indoor illumination such as an incandescent or fluorescent lamp. That is, since the IR image generated by the indoor illumination or lighting illumination is included in the IR image obtained through the image pickup device, the IR sensor may erroneously recognize the long-distance object, indoor illumination or lighting illumination as the object that exists in the sensing area.
Accordingly, in the related art, the IR image generated from the external luminous object is mixed with the IR image generated from the photometric illumination. Therefore, the accuracy of sensing an object in a sensing area is degraded, and the IR sensor is necessarily used under illumination conditions limited to minimize influence by an external luminous object.